The present invention relates to laboratory testing devices. More particularly, the present invention relates to methods and apparatuses for detecting foaming from samples.
It is known in the art to use laboratory reaction calorimeter devices to obtain design basis data for designing chemical process relief systems. Data obtained include adiabatic rates of temperature and pressure rise for very fast, runaway type reactions. These devices generally operate by heating a test sample contained in a test cell until a threshold of a reaction is detected. Once a reaction is under way, heaters are manipulated to balance heat losses from the test sample so that the sample may remain adiabatic as it reacts.
There are presently available several reaction calorimeters useful for the study of runaway reactions. An example includes the device of Fauske""s U.S. Pat. No. 4,670,404. While this device offers general utility, it may tend to be a difficult, expensive, and cumbersome device to operate and maintain due to its relatively complicated configuration. A less expensive, simpler reaction calorimeter useful for obtaining relief system design basis data is described in detail in Fauske""s later U.S. Pat. No. 5,229,075, the teachings of which are herein incorporated by reference.
Heretofore, prior art calorimeter devices, including those disclosed in Fauske""s ""404 and ""075 patents, lack means and methods for characterizing the flow regime of a material. In particular, the flow regime of a material under given reaction conditions may be generally-characterized as foamy or non-foamy. As its name suggests, foamy system behavior is generally characterized as a tendency for the liquid level to swell or foam as a reaction occurs and vapor or gas is generated in the liquid bulk. A common example of foamy behavior would be soapy water as air is blown into it; a great deal of foam results. A non-foamy system, on the other hand, does not tend to produce significant liquid level swell or foam during a runaway excursion. Water without any soap additives, for instance, does not foam appreciably as air is blown into it.
It is not possible to predict whether a material may be characterized as foamy or non-foamy when under runaway reaction conditions based on physical property data alone. Further, no known prior art calorimeter systems or other bench scale systems are equipped to make flow regime characterizations, such as a determination of whether a reaction under given conditions may be characterized as foamy or non-foamy, other than by visual means. That is, the only method by which flow regime characterization such as foamy or non-foamy classification may be made is through visual observation. As this practice is not safe or practical for a reaction under runaway conditions, observation is not a practical means of obtaining relief system design basis data.
In terms of relief system design, the characterization of a system as foamy or non-foamy is of critical importance. A foamy system presents a much more challenging system to accommodate under runaway conditions than does a non-foamy system. A foamy system generally requires larger overall capacity, with larger diameter vent piping and larger capacity down stream relief system components. Without such accommodations foamy systems may result in pressure rises that exceed vessel design pressures and cause vessel failure. As there is presently no known available practical method or apparatus for determining whether a reactive system is foamy or non-foamy, current relief system design practice is to generally assume all systems are foamy and to thus design overly conservative relief systems in many cases.
Further, for a given foamy system, there are no calorimeter devices capable of determining at what point during a reaction foamy behavior begins. Such information would be of great value, as a relief system could potentially be designed to accommodate the reaction during its non-foamy stage, thereby resulting in a less extensive, less costly system.
There are of course applications in addition to relief system design applications that have a need for determining the foaminess or flow regime of a material.
In conclusion, an unresolved need in industry exists for a method and apparatus for characterizing a material""s foaminess.
It is an object of the invention to provide a method and apparatus for characterizing a material""s flow regime as foamy or non-foamy.
It is a further object of the invention to provide a calorimeter apparatus having foam detector meas.
It is a further object of the invention to provide a foam detector apparatus.
It is a still further object of the invention to provide a method for detecting foaming from a test sample.
The apparatus of the present invention generally comprises foam detection means for detecting the presence of foam in a test sample being heated. The foam detection means of the present invention preferably comprise a detector placed above the surface level of a test sample. As foam rises from the sample it will come into contact with the foam detector. The foam detector will then send a signal to a data recording medium that records the test sample temperature at which foam was detected.
The preferred foam-detector comprises a probe with a heater for heating the probe surface, and a temperature measurement means operatively connected to the probe surface for measuring its temperature. The probe is of relatively low thermal mass, so that the surface temperature will change rapidly when contacted with cooling media. When the probe surface is in a gaseous environment over the surface of the test sample, the surface is heated to an elevated temperature above the predicted tempering temperature of the components of the sample. When foam comes in contact with the heated surface, the liquid component of the foam quickly cools the surface of the probe through latent heat of vaporization effects as the liquid turns to vapor on contact with the heated surface. Consequently, the probe surface temperature rapidly falls to a temperature near to the tempering temperature of the liquid component of the foam due to evaporative cooling effect. The temperature of the probe surface at this time should approximately correspond to the measured temperature of the liquid.
An example embodiment of the present invention comprises foam detection means for detecting the presence of foam in a sample being tested in a calorimeter. The calorimeter generally comprises a test sample container for containing a test sample, heater means for heating the test sample in the sample container, and temperature measurement means for measuring the temperature of the test sample. The foam detection means of this example embodiment are generally as described above. As foam rises from the sample being tested in the calorimeter it will come into contact with the foam detector. The foam detector will then send a signal to a data recording medium that records the temperature, time, and pressure at which foam was detected.
The method of the invention generally comprises a method for determining the flow regime of a test sample as foamy or non-foamy. The method comprises the general steps of heating a test sample in a test sample container, placing a foam detector means above the test sample surface, and detecting the presence of foam with the foam detector means.
In a preferred embodiment of the method of the invention, the step of detecting the presence of foam comprises the steps of heating a measuring surface of the detector probe to a temperature above the tempering temperature of the test sample, measuring the temperature of a measuring surface on the detector probe, and indicating the presence of foam when foam contacts the measuring surface and thereby causes the measuring surface temperature to fall to a temperature near the sample tempering temperature. Preferably, the detector probe measuring surface is comprised of low thermal mass glass.
The above brief description sets forth rather broadly the more important features of the present disclosure so that the detailed description that follows may be better understood, and so that the present contributions to the art may be better appreciated. There are, of course, additional features of the disclosure that will be described hereinafter which will form the subject matter of the claims appended hereto. In this respect, before explaining the several embodiments of the disclosure in detail, it is to be understood that the disclosure in not limited in its application to the details of the construction and the arrangements set forth in the following description or illustrated in the drawings. The present invention is capable of other embodiments and of being practiced and carried out in various ways, as will be appreciated by those skilled in the art. Also, it is to be understood that the phraseology and terminology employed herein are for description and not limitation.
The objects of the invention have been well satisfied. These advantages and others will become more fully apparent from the following detailed description when read in conjunction with the accompanying drawings.